Conventionally, an image forming apparatus such as a digital MFP (Multi-Function Peripheral), a copier, a printer and the like forms an image on paper and then discharge the paper. Further, a post processing apparatus (finisher) is arranged to be connected with a paper discharge section of the image forming apparatus main body to carry out post processing on the paper on which an image is formed. The post processing apparatus includes an apparatus which staples or perforates the paper.
For example, in a case of forming perforations in a direction parallel to a paper conveyance direction, a perforation processing position is set by a user, and the user moves a perforation cutter to the processing position. Further, the perforation cutter is fixed at an angle parallel to the paper conveyance direction.
However, the user has to adjust the position of the perforation cutter according to the paper size. Further, there is a case in which the paper conveyed to the post processing apparatus is inclined (hereinafter referred to as skew) with respect to the conveyance direction. If the paper is skewed, there is a disadvantage that the perforations are formed at positions different from the desired processing position.